Scientists say they now know why smoking marijuana sends you rummaging through the pantry, looking for that bag of potato chips to satisfy your pot "munchies."
There's plenty of anecdotal evidence suggesting smoking pot throws people into "snack-binge" mode, and Yale University researchers decided to investigate pot's active ingredients to find out why.
"Everyone knows that if you smoke dope after Thanksgiving dinner you will still go back and eat more -- sometimes much more," says Tamas Horvath, a professor of neurobiology in the university's school of medicine. "We were interested to find out why."
Horvath and his colleagues use lab mice -- effectively getting them stoned -- as part of their studies of brain circuits involved in hunger and satisfaction.
The active ingredients in marijuana, chemicals known as cannabinoids, seem capable of causing certain brain cells involved in hunger and satiety to switch their functions, the researchers report.
"It's like pressing a car's brakes and accelerating instead," Horvath says.
The cannabinoids activate cells in the brain's hypothalamus called pro-opiomelanocortin (POMC) neurons, which regulate appetite.
"We were surprised to find that the neurons we thought were responsible for shutting down eating, were suddenly being activated and promoting hunger, even when you are full. [Marijuana] fools the brain's central feeding system."
Further researcher revealed that cannabinoids can alter what kinds of chemical POMC neurons release. Normally, the neurons release MSH, an appetite-suppressing chemical, but when a person smokes marijuana the active ingredient causes the POMCs to release beta-endorphin, an opioid which accelerates hunger.
"The whole circuitry turns upside down," Horvath says of the discovery that marijuana can modify a brain circuit from one responsible for telling the body that it's full to one that prompts the body to keep on eating.
The findings might be turned to good medical uses, the researchers speculate, such as helping cancer patients or people with AIDS who often suffer a loss of appetite during their treatment, as a way to treat people with anorexia.
They also suspect altered POMC functionality may be involved in diabetes or in people who are obese, suggesting possible treatment avenues.
There have been previous studies into marijuana's "munchies" effect; a decade ago, one study found a drug called rimonabant could turn off the brain circuit that marijuana turned on.
The drug was offered as an anti-obesity treatment under the brand names Acomplia and Zimulti, but they were taken off the market because of serious side effects including depression.
